1. Field of the Invention
This invention relates to a seam for joining together the ends of woven fabric to form an endless belt. It is applicable more specifically to joining the ends of woven synthetic dryer fabrics as used in the dryer section of paper making machines and is particularly applicable to joining the ends of those dryer fabrics which have very pliable or multifilament yarns in at least the machine direction of the fabric.
2. Description of Prior Art
Dryer fabrics are usually woven of natural or synethethic fibres such as, for example, polyesters, nylons, acrylics, bulked or of interwoven layered structure to produce a heavy woven fabric which can be, for example, from about 1/32 to about 1/8 of an inch thick. Dryer fabrics are supplied in various widths from about 5 feet to about 30 feet depending on the width of the paper machine, and in length from about 40 feet to about 350 feet.
It is common practice to weave the dryer fabric as a long wide flat single piece and then join the ends on the machine to make an endless belt. There are several known methods of making the joint or seam as it is called. In one method, each end of the fabric is provided with a set of metal clipper type loops. In another method, metal or plastic loops are sewn into the ends which have been reinforced to prevent unravelling. In still another method, cross machine strands(weft) are removed near the ends of the fabric and the ends are folded back in such a way that warp loops in the unwefted sections project. In each case the joint is completed when the array of loops at one end is intermeshed with the array of loops at the other end and brought into register to form a tubular passage through which a hinge pin or pintle wire is inserted.
These above known conventional methods of making a seam in heavy dryer fabrics all have the disadvantage of either producing a gross lump which causes sheet disturbance and marking or an almost complete mesh blockage. Either of these features being objectional from the point of view of fabric wear or quality of sheet.
Another type of seam that has been successfully used in dryer fabrics having monofilament longitudinal strands capable of retaining a stable crimp is a loop type wherein the loops are formed at each end edge in the following manner. Projecting longitudinal (machine direction) strands from which cross strands have been removed at each end of the fabric are interwoven again into a plurality of added cross strands comprising either the removed or similarly crimped strands in the seam area. Selected longitudinal strands are looped over a forming rod at the end edge of the plurality of added cross strands and are woven back into the added cross strands to meet the ends of adjacent machine direction strands which have been woven part way into the group of added cross strands and terminated. The surplus ends of these longitudinal strands are subsequently clipped off at the surface of the cloth in the seam area where they meet to form abutting terminations. Those longitudinal strands that are not looped over the forming rod are simply looped tightly over the last added cross strand and similarly woven back into the seam area to meet an adjacent longitudinal strand at an abutting termination. Abutting termination points of the longitudinal strands are positioned in a predetermined uniform pattern throughout the seam area to avoid having them clustered together where they might obstruct the mesh unduly or cause a surface lump or a weakness of tensile strength in the joint.
A forming rod is looped in as described above at each end of the fabric and when it is required to join the ends of the fabric on the paper machine, the forming rods are withdrawn, the loops are intermeshed and the hinge pin (pintle wire) is inserted.
The advantage of this type of seam is that the continuity of mesh at each end, right up to the formed loops, is maintained without a layered thickening and without a discernible mesh blockage. The success of making such a seam depends upon stability of crimp in the longitudinal strands. The strength of the seam is controllable and determined by the number and strength of the looped longitudinal strands and by the number of added cross strands through which the crimped longitudinal strands are interwoven.
While this type of seam is ideal for joining the ends of dryer fabrics having monofilament longitudinal strands capable of retaining a crimp, it has not been possible to apply the method to dryer fabrics having, for example, multifilament longitudinal strands, which are generally pliable and do not have a stable cross-sectional dimension and crimp, although many attempts have been made to seam them in this way because of the physical and economic advantages which the multifilament strands offer.
The multifilament strands are generally made up of a large number of single fibers of very small diameter, twisted together to form a single flexible strand. Since these strands are normally quite limp the fabric made from them is generally coated with a thermo-setting resin material to stiffen it so that it will resist distortion in its own plane. While the coating of resin material does tend to make the multifilament strands less pliable it is generally only effective in this respect in the woven state and once disturbed, as when the strands are unwoven, the coating comes off and they again become pliable.
The problem encountered when attempting to seam fabrics comprising longitudinal multifilament or other strands incapable of holding a crimp is that the crimp is not stable after a strand is unwoven and it does not assume exactly the same configuration when re-woven in the seam area, thus the spacing of both the added cross strands and the longitudinal strands is affected. Multifilament strands tend to splay out and become bulky as well as limp and attempts to force them into place when re-weaving causes the seam area to become lumpy. Also, a point is soon reached, after weaving a number of multifilament strands, when it is impossible to force any more strands into the mesh. Attempts to alleviate this condition by cutting out say every 3rd, 4th or 5th multifilament strand reduces the lumpy effect to some extent but does not contribute to retention of uniform spacing of the additional cross machine strands and so the advantage of cutting out some of the longitudinal strands is lost. Further, limp longitudinal strands do not retain crimp sufficiently well to lock them into the added cross strands, through which they are interwoven and they tend to pull out of the mesh, thus weakening the seam.